1. Field of the Disclosure
The present invention relates to a grinding machine for grinding workpieces, in particular for the simultaneous grinding independently of one another of two workpieces which are arranged in a tightly adjacent manner, and to a method for grinding workpieces on a holder, in particular for the simultaneous grinding independently of one another of two workpieces which are arranged in a tightly adjacent manner.
2. Description of Related Art
Grinding machines of this type are known, for example, from the brochure “CamGrind—Produktionslösungen für das Schleifen von Nockenwellen” [“CamGrind—production solutions for the grinding of camshafts”] from the firm Studer Schaudt GmbH, Stuttgart from October 2006. Here, for example, the model “CamGrind L” on pages 7 and 16 has a grinding device with two spindle sets which consist in each case of a large and a small grinding disk and are designed, above all, for grinding camshafts. By way of the large grinding disk, first of all the cams are preground here and the bearing seats are machined by means of high power, whereas the small grinding disk serves to grind the cam shapes to a finish or else to grind the bearing seats. In order to machine the camshaft, the latter is arranged on a workpiece holding device which, on one side, has a workpiece spindle head which sets the camshaft in the desired rotation about its longitudinal axis and, on the other side, has a tailstock which ensures that the camshaft is always oriented and centered during the machining. The grinding disks and the corresponding grinding spindles can be moved relative to the camshaft within the x-z plane, with respect to said components of the workpiece holding device which are stationary as a rule. The grinding of the cams directly on the shaft is carried out for the purpose of accuracy, in order that the cams are shaped exactly in relation to the shaft.
When the axes or directions x and z are mentioned in the previous or following text, this always means the two axes which define the plane which forms the machine bed. Here, the z-axis extends parallel to the longitudinal extent of the workpiece, here, for example, of the camshaft, and the x-axis extends as an axis which is perpendicular with respect to the former, which therefore corresponds to a movement of a tool toward or away from the corresponding workpiece from the side. Furthermore, a direction which is perpendicular with respect to the x-axis and z-axis is called the y-axis or y-direction. As a result, it extends perpendicularly with respect to the machine bed.
In order for a selection to be possible between the grinding disks in the grinding machine, the grinding spindle of the small grinding disk is arranged correspondingly on the grinding spindle of the large grinding disk, in such a way that it can be pivoted about the rotational axis of the large grinding disk, or of the corresponding grinding spindle. This principle is already known from DE 195 16 711 A1. The aim here is to achieve a considerable space saving as a result of this spindle set, that is to say by the combination of the large and the small spindle with the corresponding pivoting mechanism.
In the known grinding machines of the series “CamGrind L” which are mentioned in the introduction, this is realized in such a way that the grinding spindles with the small grinding disk are arranged on the spindle block of the large grinding spindle in such a way that the small grinding disk comes to lie approximately 150 mm in the direction of the z-axis behind the large grinding disk.
If a simple grinding spindle set is used which consists of a large and a small grinding spindle, this represents an appropriate arrangement, since the space requirement of the grinding spindle set thus remains as low as possible.
If, however, it is desired to use two grinding spindle sets, as is the case, for example, in the model series “CamGrind L” which is mentioned in the introduction, the problem arises that, in contrast to the large grinding disks, the small grinding disks cannot be moved as closely to one another as desired, with the result that, after positioning of one grinding spindle set and the small grinding disk arranged thereon on a workpiece, there is a corresponding region along said workpiece, which region cannot be reached by the other small grinding disk on the other grinding spindle set. This spacing arises from the positions of the small grinding spindles on the large grinding spindles and would therefore be approximately 300 mm for the model “CamGrind L” which is mentioned in the introduction.
As a result, this mutual impeding of the grinding spindle sets makes more complicated programming of the entire grinding procedure necessary, in order to keep the losses in the efficiency of the grinding machine on account of this impeding as low as possible. Moreover, the time requirement as a result of this mutual impeding is greater than it should be according to expectations when two grinding spindle sets are used. This would ideally be at least half the time as when only one grinding spindle set is used.
Furthermore, it has also been shown, if only one grinding spindle set is used, that, in some positions, the large grinding disk can already collide with the workpiece spindle head or the tailstock when the small grinding disk is to carry out machining and grinding operations which lie very close to the center point of the rotational axis of the workpiece.